Less active and not eating are general signs that the fish do not feel well. Almost any problem will start showing up as less active and not eating. The 'spots' that I see in the pictures look more like Flavobacteria columnare than anything else. However, a minor injury can start growing fungus, and that also looks like this in the early stages. If you treat with antibiotics that target Gram negative bacteria these meds generally have little or no effect on the nitrogen cycle bacteria. If you decide to treat them, then use the antibiotics per label directions, and I would get a bottle of nitrifying bacteria also and use this after the medication to re-boost the population of beneficial bacteria.